Torque sensors made from amorphous magnetic alloy having magnetostriction, or Fe-based alloy having magnetostriction, have been known. For example, Published Unexamined Japanese Patent Application No. Hei 3-26339 discloses a torque sensor which has a metal shaft whereon an amorphous magnetostrictive alloy ribbon sensitive to stress is glued. Elongated slits are formed on the amorphous magnetostrictive alloy ribbon of the torque sensor. The angles of the slits are +45.degree. and -45.degree. to the shaft longitudinally, if the magnetostrictive alloy ribbon adheres to the shaft's surface. FIG. 10 shows an amorphous magnetostrictive alloy ribbon 21 by the prior art. The letters in the figure are described as follows: a'=35.8 mm (i'=1 mm, h'=1 mm) long, b'=25.0 mm (c'=10.5 mm, d'=10.5 mm, e'=1 mm, f'=2 mm, g'=1 mm) wide. The width of slit s is 0.3 mm. The repetition pitch (spacing between the two slits) t is 2.0 mm. The angle of the slits (.epsilon.) is 45.degree.. Longitudinal a' is circumferential in use for the torque sensor. The slits are used to detect the torque's direction. Coil means are arranged outside of the amorphous magnetostrictive alloy ribbon in order to detect magnetic property. By the application of torque to the shaft, tensile and compression stresses are generated at +45.degree. and -45.degree. to the shaft's surface longitudinally. This results in changes in magnetic property of the slits at +45.degree. and -45.degree. on the amorphous magnetostrictive alloy ribbon. The difference of the changes in magnetic property is detected by coil means, thus the direction and magnitude of the torque is detected.
Manufacturing methods of such a torque sensor are explained below:
forming by force an amorphous plate cylindrically and gluing it; or
forming an amorphous plate cylindrically by annealing to adjust almost the diameter of the shaft, and then gluing it.
In the former method, a flat metal ribbon is formed cylindrically and glued. Therefore, plural rows of slits formed on the metal ribbon might be distorted when bent, which is one of the causes of unevenness or damage to the metal ribbon. In the latter method, a metal ribbon is fixed to a metal cylindrical jig and annealed. A problem with this method is distortions of the slits in the process of fixing the ribbon to the jig, which resulted in damage to the ribbon. The encircled parts of a metal ribbon 22 in FIG. 11 (u.sub.1 to u.sub.7) show that certain parts of the slits are often damaged, which might lead to a low yield of the product. With respect to the magnetic anisotropy provided by the slits, inner distortions are often caused even if there is no damaged part. As a result, good linear output is not obtained over a wide range of torque.